The invention relates to operation microscopes, particularly for operations upon the eye, and to the control of field illumination for such operations.
In ophthalmic microsurgery, field illumination can damage the retina even though the focus of surgery is in a plane removed from the retina, for example an operation such as a radial keratotomy upon the cornea. It is, of course, the surgeon's responsibility to make sure that, even when performing a particular operation which does not involve the retina, he nevertheless avoids damaging exposure of the retina to his illumination. The problem is aggravated by the fact that illumination brightness will vary in the course of a particular procedure, in that bright illumination is only needed for short intervals, and there can be intervals of no illumination and/or of reduced illumination. Retinal damage is a function of time integration of the different levels of illumination, over the full course of a given procedure; the damage becomes irreparable once a tolerance level of the integrated value has been exceeded. And the surgeon's skill, experience and intuition have had to be the basis for avoiding retinal damage, by executing operative steps with greatest efficiency and dispatch.